Display devices utilizing liquid crystal light modulation

ABSTRACT

Optical display devices for converting electrical intelligence into optical images with the use of a shutter device comprising a layer of liquid crystal material sandwiched between opposing parallel plates coated with transparent conducting films. These plates, with the liquid crystal material therebetween, are disposed between and parallel to a pair of polarizers such that when an electrical potential is established across the conducting films and the liquid crystal layer, the device will change from a light transmitting to opaque medium, or vice versa, depending upon the orientation of the two polarizers. By forming the two conducting films in the shape of a desired optical image, that image can be made to appear or disappear, depending upon whether a potential is established between the conducting films. Furthermore, by creating separate conducting areas, as by etching the conducting films, any given number of conductive regions can be switched ON while other regions are not affected to produce any one of a number of different images with the same liquid crystal sandwich assembly. Finally, by etching a pattern of strips of transparent conducting material on the two opposing plates, by orienting the strips on the respective plates at right angles to each other, and by selectively applying pulsed voltages to the strips on the respective plates, the area of liquid crystal layer can be scanned point by point to produce with the same display any one of a number of optical images such as numerals, letters or the like. The invention has particular utility in computer and calculator read-outs, for example, since the display can be energized at a voltage level compatible with that used to drive the integrated circuitry used in such devices without the necessity for relatively high voltage driving circuitry.

CRYSTAL LIGHT MODULATION [75] Inventor: James L. Fergason, Kent, Ohio[73] Assignee: International Liquid Xtal Company,

Cleveland, Ohio [22] Filed: Apr. 22, I971 [21] Appl. No.: 136,441

Related US. Application Data [63] Continuation-in-part of Ser. No.113,948, Feb. 9,

1971, abandoned.

52 US. Cl ..3s0 1so, 252/408, 340/324 R, 350/160 LC [51] Int. Cl ..G02f1/18 [58] Field of Search ..350/150, 157, 160; 252/408; 340/324 R 5 6]References Cited UNITED STATES PATENTS 3,597,044 8/1971 Castellano..350/l60 3,499,702 3/1970 Goldmacher et al.. ....350/150 3,581,0025/1971 Dodds ....350/l60 3,597,043 8/1971 Dreyer..... ....350/l503,625,591 12/1971 Freiser ..350/l50 3,576,364 4/1971 Zanoni ..350/l603,612,654 10/1971 Klein ..350/l60 Primary Examiner-Edward S. BauerAttorney-Brown, Murray, Flick & Peckham 5 7 1 ABSTRACT Optical displaydevices for converting electrical intelv, 51 May 8,1973

conducting films and the liquid crystal layer, the

device will change from a light transmitting to opaque medium, or viceversa, depending upon the orientation of the two polarizers. By formingthe two conducting films in the shape of a desired optical image, thatimage can be made to appear or disappear, depending upon whether apotential is established between the conducting films. Furthermore, bycreating separate conducting areas, as by etching the conducting films,any given number of conductive regions can be switched ON while otherregions are not affected to produce any one of a number of differentimages with the same liquid crystal sandwich assembly. Finally, byetching a pattern of strips of transparent conducting material on thetwo opposing plates, by orienting the strips on the respective plates atright angles to'each other, and by selectively applying pulsed voltagesto the strips on the respective plates, the area of liquid crystal layercan be scanned point by point to produce with the same display any oneof a number of optical images such as numerals, letters or the like. Theinvention has particular utility in computer and calculator read-outs,for example since the display can be energized at a voltage levelcompatible with that used to drive the integrated circuitry' used insuch devices without the necessity for relatively high voltage drivingcircuitry.

11 Claims, 8 Drawing Figures PATENTEB HAY 81975 SHEET 1 (IF 2 A rrorneysPATENTED 81973 3.731886 SHEET 2 UP 2 3 BITR N INVERTERS AND COUNTERLEI/EL SET a 0 A 1 0 B ascour' C 86 74/ 02 MATRIX D 76 E 72 75 j F 6 gzFF INH/B/f READ mvmrms ONLY AND 94 INHIBIT MEMORY Lfl/EL ssr 92 90COMPUTER ONE FRAME F/G. 7.

PER/0D INVERTER ONE STEP our urs PER/0D ISMS A +.9l 8 U 0 M C LF 0 U ROWDRIVER U aurpurs E L! F L] n n -+6V H n COLUMN DRIVEN J n n J our/ urs00050 K F1 F1 70 DISPLAY THE L [-1 NUMERAL rwo M n l l f J m/vs/v TOR.

JAMES L.FERGA$0N y A W 4 m $2M? A H orneys DISPLAY DEVICES UTILIZINGLIQUID CRYSTAL LIGHT MODULATION CROSS-REFERENCES TO RELATED APPLICATIONSThis application is a continuation-in-part of copending application Ser.No. 113,948, filed Feb. 9, l97l and now abandoned in 'the name of JamesL. Fergason as inventor and entitled Liquid-Crystal Non-Linear LightModulators Using Electric and Magnetic Fields."

BACKGROUND OF THE INVENTION As is known, there are a large number oforganic chemical compounds that will, within a particular temperaturerange, exhibit nematic-phase liquid crystals. These compounds are liquidin the sense that their molecules are not dissociated as in a gas nor sotightly bound within a structure as to constitute a solid. At the sametime, they are said to be crystalline, in that there is a particularordering to the orientation of the molecules, as is sometimes evidencedby peculiar optical effects.

It is also known that when a nematic-phase liquid crystal material issandwiched between transparent plates that have been rubbed, each ofthem unidirectionally and on the surface in contact with thenematic-phase liquid crystal material, there is obtained aliquid-crystal unit whose optic axis lies in the direction ofunidirectional rubbing. If two rubbed plates with the rubbed directionsat right angles to each other are used to contain a nematic liquid, thenthe resulting effect will be an optical media which rotates the plane ofpolarization by 90. Similarly, if the two rubbed directions are aligned45 with respect to each other, the resulting nematic liquid will rotatethe plane of polarized light by 45. Any amount of rotation between and90 can be obtained by using such rubbed surfaces.

By using nematic materials which align parallel with an applied electricor magnetic field, the nematic alignment is disrupted at a low fieldlevel. The mechanism involved resides in the fact that the liquidcrystal is elastically deformed by surface constraints such that thelong axis of the nematic material is oriented in a helical manner. Ifthe direction of the molecules at the center of the sample is changedsuch that they are parallel with an applied field which is also parallelwith the twist direction, no torque is exerted on opposite sides of theliquid crystal and it no longer remains twisted. This will occur just asthe molecules at the center of the nematic cell become parallel to theapplied electric field. Therefore, it will occur at a very sharp fieldlevel resulting in bistable operation. The voltage required isdetermined by the relationship:

where k is an elastic constant and A t is the difference in electricalpolarizability parallel and perpendicular to the long axis. When such adevice with a 90 twist is placed between parallel polarizers, no lightwill be transmitted at zero voltage and it will be the equivalent of twocrossed polarizers. When an electric field is applied to the device, thestructure will untwist at a well defined voltage and allow lighttransmission. If, however, the same device is placed between crossedpolarizers, then at zero voltage light is transmitted and the polarizerswill effectively act as though they are parallel. However, with theapplication of a critical voltage, the plane of polarization will nolonger be rotated and no light will be transmitted. Thus, the deviceacts as a shutter for transmitted light. The liquid crystal materialused must be nematic and must have a positive dielectric anisotropy. Atthe same time, the material must be nematic over a substantialtemperature range, including the room temperature range. A suitablematerial for this purpose is described in copending application Ser. No.113,948, filed Feb. 9, 1971, of which this application is acontinuation-inpart. It comprises a mixture of 40 percentbis-(4'-n-octyloxybenzal)-2-chlorophenylenediamine, 50 percentp-methylbenzal-p'-n-butylaniline and 10 percentpcyanobenzal-p-n-butylaniline.

SUMMARY OF THE INVENTION In accordance with the present invention,liquid crystal material sandwiched between rubbed transparent plates anddisposed between polarizers isutilized to construct devices whichdisplay information spatially. Specifically, there is provided a devicefor converting electrical intelligence into an optical image comprisinga layer of liquid crystal material disposed between transparent parallelplates which are coated on only selected areas thereof with films oftransparent conducting material, polarizers on opposite sides of theplates and essentially parallel thereto to provide a sandwich structurethrough which light can pass, and means for establishing a potentialdifference between conducting transparent films on the respective platessuch that areas of the sandwich structure will transmit light whileothers will not to form an optical image.

In one embodiment of the invention, an optical image is formed byetching conductive glass in a pattern which represents a number orsymbol. In another embodiment, separate conducting areas are createdsuch that any number of conductive regions can be switched ON whileother regions are not affected to produce any one of a number ofdifferent images.

In accordance with still other embodiments of the invention, a patternof strips of transparent conducting material is etched on the twotransparent plates on opposite sides of a film of nematic liquid crystalmaterial. The strips are then rubbed in such a manner that the rubbeddirection is parallel to the strips. The two transparent plates areplaced together with the strips perpendicular. By applying pulsedvoltages to a pair of crossed strips on the respective glass plates,only that region where the strips cross will be transparent, forexample, while the remainder of the liquid crystal is opaque. Thus, itis possible to scan a region point by point. If the strips on one plateare called rows while those on the other columns, each row can bescanned by applying a field pattern to the columns. With properadjustment of voltages, it is then possible to scan such a system. Theoutput of such a system is binary, being either ON or OFF.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 is a schematic view of a liquid crystal unit made in accordancewith the present invention;

FIG. 2 is aview illustrating the manner in which the transparent platesof the liquid crystal unit of FIG. 1 are rubbed at right angles withrespect to each other;

FIG. 3 is a schematic illustration showing the manner in which polarizedlight passes through the liquid crystal unit of the invention;

FIG. 4 illustrates one manner in which an optical image may be producedwith the liquid crystal unit of the invention;

FIG. 5 illustrates the manner in which rows and columns of transparentconducting material may be etched on opposing transparent plates whichbound a layer of liquid crystal material to effect an array which can bescanned;

FIG. 6 is a schematic circuit diagram illustrating one manner in whichan array, such as that shown in FIG. 5, can be scanned;

FIG. 7 comprises waveforms illustrating the operation of the circuitryof FIG. 6; and

FIG. 8 illustrates still another manner in which conductive films onopposing transparent plates can be etched to provide different opticalimages.

With reference now to the drawings, and particularly to FIG. 1, there isshown a liquid crystal unit 10 comprising a first transparent plate 12,preferably of glass, and a second transparent plate 14, also of glass,and extending parallel to the plate 12. The plates 12 and 14 are spacedapart by suitable spacers, not shown, by approximately 0.25 to 2 mils;although the spacing may in some instances be as little as 0.1 to 0.05mil. This space is filled with a nematic-phase liquid crystal materialwith a positive dielectric anisotropy preferably of the kind hereinaboveindicated, namely one comprising major portions such as percent to 80percent each of bis-(4'-n-octyloxybenzal-2-chlorophenylenediamine andp-methylbenzal-p'-n-butylaniline, these making up about 60 percent to 97percent of the total composition and p-cyanobenzal-p-n-butylanilinecomprising the remaining 3 percent to 40 percent. This material, asmentioned above, is described in copending application Ser. No. 113,948,filed Feb. 9, I971.

Disposed on the interior surfaces of the transparent plates 12 and 14and in contact with the liquid crystal layer 16 are coatings l8 and 20of thin transparent electroconductive material, such as the known tinoxide or indium oxide coatings. These coatings are quite thin and highlyresistive, for example, on the order of 150 ohms per unit square orabove, and possibly as high as 5,000 to 10,000 ohms per unit square. Itis desirable that the transparent electroconductive coating be of thekind that is applied at relatively low temperatures such as about 500F,by the process of cathode-sputtering in a vacuum, so that dangers ofwarpage may be safely avoided.

In FIG. 2, there is shown a view of the plates 12 and 14 which maycomprise flat glass on the order of about one-eighth inch thick havinglayers 18 and 20 of transparent conducting material deposited on thefacing surfaces thereof. In the preparation of a liquid crystal unit,the layers of transparent conducting material that are in contact withthe nematic-phase liquid crystal material must be prepared by beingstroked or rubbed unidirectionally with, for example, a cotton cloth.The

direction of rubbing on the respective plates 12 and 14 is indicated bythe lines 22 and 24 in FIG. 2; and it will be appreciated that thedirections of rubbing on the respective plates are at right angles toeach other. The effect of this is to produce a twisted nematic structureas explained above. In this respect, the molecules in a nematic-phaseliquid crystal material are each long and straight, and they tend to lieparallel, like logs in a river or straws in a broom. Their parallelismis statistical, rather than perfect and exact. They are free to movewith respect to one another, and there are some that are at a smallacute angle with respect to the main stream, and a few others that areat any given moment in a position even less consonant with the bulk ofthe others. A property of the nematic-phase liquid crystal materials isthat the molecules in the vicinity of a rubbed surface tend to alignthemselves with it. Thus, the molecules nearest the surface of the plate12, for

example, are inclined to orient themselves parallel with the lines 22,nd those nearest the surface of plate 14 are inclined to orientthemselves parallel to the lines 24. The structure is fluid and active;and under conditions of no applied voltage, the molecules in the variouslayers that are parallel to the surfaces of plates 12 and 14 arrangethemselves in what may be considered a number of layers of suitableintermediate mainstream directions, ranging from one close to parallelto the lines 22 (a short distance from the surface of plate 12) throughone at about a 45 angle with respect to both the lines 22 and 24 (atabout the midpoint of the distance between the plates 12 and 14); and onto one close to parallel with the lines 24 (a short distance from thesurface of plate 14).

The effect of the liquid crystal unit on polarized light directedthrough the plates 12 and 14 and polarized parallel to the lines 22, forexample, is that the unit effects a rotation of the plane ofpolarization of the light as it passes through the unit, so that thelight emanating from the surface of the plate 14 is plane polarizedparallel to the lines 24. However, it would not matter if the planepolarized light impinging upon the plate 12. for example, were polarizedin parallel planes that were at some angle with respect to the lines 22.The same effect of rotation of the plane of polarization is obtained.The extent of rotation does not need to be Any desired extent ofrotation may be obtained, merely by properly orienting theunidirectionally rubbed surfaces on the plates 12 and 14. However, whenthe directions of rubbing are at right angles to each other, the extentof rotation is 90.

The effect of the crystal unit 10 on polarized light is schematicallyillustrated in FIG. 3. Thus, a source of unpolarized or natural light at26 impinges upon a conventional polarizer 28 which polarizes the lightindicated by the broken lines 30. This polarized light, as it passesthrough a liquid crystal unit such as unit 10 shown in FIG. 1, will berotated through 90 so that the polarized light is then polarized in aplane indicated by the broken lines 32. This polarized light will thenpass through a second polarizer 34 adapted to pass polarized light in aplane which is rotated at 90 with respect to the plane of polarizationof polarizer 28, as indicated by the broken lines 36. Hence, under theconditions described, the polarized light passing through polarizer 28will be rotated through 90 in unit 10 and will then pass through thepolarizer 34. On the other hand, if the polarizer 34 should be rotatedsuch that the plane of polarization indicated by broken lines 36 isparallel to the plane of polarization of polarizer 28, then no lightwill pass through polarizer 34.

Now, if an electrical potential, on the order of 5 volts or greater, isapplied between the conducting films 18 and 20, the liquid crystal unitwill no longer rotate the plane of polarization through 90. In thearrangement shown in FIG. 3, for example, application of a suitablepotential to the conducting films 18 and will cause the polarizer 34 toblock the transmission of light. It can thus be seen that the deviceacts as an optical shutter. On the other hand, if the polarizer 34 isoriented 90 with respect to that shown in FIG. 3, no light will betransmitted in the absence of a potential applied between the films 18and 20; whereas light will be transmitted when a potential is appliedthereacross.

Referring again to FIG. 1, the polarizers 28 and 34 are in the form offlat sheets, preferably dichroic polarizing sheets of the typemanufactured by Polaroid Corporation. However, other types of polarizersmay be used to suit requirements. For that matter, instead of usingseparate polarizing sheets or separate polarizers, the polarizers can bedirectly incorporated into the device 10. In this regard, the surfacesof the conductive coatings l8 and 20, for example, can be rubbed andtreated with a solution of a dye which forms a dichroic film asdescribed in Dreyer US. Pat. Nos. 2,544,659, 2,524,286 and 2,400,877.Such a solution can comprise a 4 percent aqueous solution of methyleneblue. By coating the rubbed surface of the conductive film 18 or 20 withthis dye solution and allowing it to dry, a dichroic film will bedeposited on the surface with a thickness on the order of about 1micron. By placing the liquid crystal material as described abovebetween the two rubbed plates treated with polarizing material, a singlelayer material will result which will have the complete systemincorporated. Thus, the liquid crystal will align up parallel to therubbed direction. When these are placed together, the polarizers will becrossed but with the liquid crystals between there will be a maximum oftransmission. When an electric field is applied to the conductinglayers, the liquid crystal layer will become opaque. This will occur atapproximately 5 volts field since the dye represents but a smallfraction of the insulating layers between the electrodes.

In FIG. 1, the means for applying an electric field between theconducting films l8 and 20 is shown as a conventional battery 38 adaptedto be connected into the conducting films l8 and 20 through switch 40.Alternatively, however, the same effect can be achieved (i.e., changingthe plane of the polarized light passing through the device 10) with theuse of a magnetic field in which the lines of flux extend perpendicularto the surfaces of the plates 12 and 14 as indicated by the north andsouth pole indications of FIG. 1. However, as will become apparenthereinafter, the use ofa magnetic field in most displays is impracticalbecause of the difficulties in localizing such a field.

With reference now to FIG. 4, one type of optical display which can beprovided with the liquid crystal device 10 of FIG. 1 is shown. It againcomprises a pair of transparent plates 42 and 44 having their opposingsurfaces rubbed in directions at right angles to each other and betweenwhich a layer of nematic liquid crystal material of positive dielectricanisotropy is disposed. The resulting sandwich is then placed betweenpolarizers as in FIG. 1, or the facing surfaces of the plates 42 and 44are treated to form a dichroic film as described above. In this case,however, the conducting films 46 and 48 are in the form of the numeral4. Assuming that the plates 42 and 44 are assembled with polarizers inthe arrangement of FIG. 3 and that switch S2 is closed to apply apotential from battery 50 across the films 46 and 48, the area coveredby the films will be opaque while the area around the conducting films46 and 48 will transmit light. Assuming that a white background isbehind the assembled plates 42 and 44 with liquid crystal material andthat the plate is viewed from the side opposite the white background,the effect will be to produce the numeral 4 in black-onwhite. Of course,when the switch 52 is again opened, the device will be totally lighttransmitting and no numeral or other optical image will appear to theeye of the observer.

The device of FIG. 4, while workable, can produce only a single opticalimage such as a numeral or letter within the area encompassed by plates42 and 44. A system for producing any desired numeral, letter or otherimage within the same area is shown in FIGS. 5-7. The system againincludes two plates 54 and 56 (FIG. 5) having facing surfaces which arerubbed at right angles with respect to each other, the space between thetwo surfaces being filled with a layer of nematic liquid crystalmaterial of positive dielectric anisotropy. The mating surfaces of theplates 54 and 56 are again coated with a conducting film; but in thiscase, the plate 54, for example, is etched, utilizing conventionalphotoresist masking techniques, to provide five vertical columns 58 eachhaving seven enlarged areas 60 spaced along its length. In a somewhatsimilar manner, the plate 56 is coated and then etched to provide sevenhorizontal rows 62 each provided with five enlarged area sections 64 ofconducting film material between its ends. The plates 54 and 56, whenfacing each other with a layer of liquid crystal material therebetween,are positioned such that the enlarged area portions 60 on the plate 54are aligned with or overlie the enlarged area portions 64 on the plate56. The ends of the strips or columns 58 on the plate 54 are connectedto five electrical leads 66. Similarly, the ends of the strips orhorizontal rows 62 on plate 56 are connected to a second set of sevenelectrical leads 68.

The manner in which an assembly formed ofthe plates of FIG. 5 can beused to produce various images is shown in FIGS. 6 and 7. The assembleddevice comprising plates 54 and 56 with a layer of nematic liquidcrystal material therebetween of positive dielectric anisotropy andsuitable cross polarizers is indicated in FIG. 6 by the referencenumeral 70. The circles on device represent overlapping enlarged areaportions 60 and 64 formed in the columns 58 and rows 62, respectively.

Clock pulses for the display are supplied from an oscillator 72typically having a frequency of about 960 hertz. These pulses areapplied to a flip-flop circuit 73, the output of the flip-flop circuitbeing fed to a conventional three-bit ring counter 74 which producespulses on leads 76, 78 and 80, those on lead 76 being divided by two,those on lead 78 being divided by four and those on lead 80 beingdivided by eight. The pulses on leads 76-80 are applied to a decodingmatrix 82 in accordance with well-known techniques to produce pulses onoutput leads 84 which are displaced in phase with respect to each other.These are applied through inverters 86 and leads 68 to the respectivehorizontal rows 62 which are identified by the letters AG.

The outputs of the inverts 86 appearing on leads 68 are identified aswaveforms A through G in FIG. 7. During one frame period, a pulseappears on each of the rows in succession. Thus, the pulse in waveform Ais applied to the top row first, followed by a pulse applied to thesecond row, followed by a pulse applied to the third row, and so on. Thetime required for pulses in waveforms AG to be applied in succession toeach of the rows is referred to as one frame period and may typically be16 microseconds; however the frame period may be any desired timeinterval. depending upon the size of the display and the number ofhorizontal rows employed. Note that the pulses in waveforms AG are ofnegative polarity. These pulses are applied to the rows in successioncontinuously regardless of the optical image, such as a numeral orletter, which it is desired to produce.

The pulses on leads 76-80 are also applied to a readonly memory unit 88connected, for example, to computer circuitry 90 or the like. The pulseson leads 76-80 activate the read-only memory unit 88 to apply to leads92 a succession of pulses representative of a particular numeral, letteror other image to be displayed. These are applied through inverters 94and capacitors 96 to the vertical rows 58 which are identified by theletters I-I-M. It will be assumed that the background behind the unit 70is white and that the liquid crystal sandwich including polarizers onopposite sides of the liquid crystal layer normally transmits polarizedlight in the absence of the application of an electrical potentialapplied across the liquid crystal layer. That is, the arrangement ofFIG. 3 is employed. In order to produce the numeral 2, for example, onlythose areas colored black in FIG. 6 between the strips 58 and 62 shouldhave electrical potentials applied therebetween, whereby these areaswill be opaque and appear black when viewed by an observer. In order toaccomplish this effect, the waveforms H-M of FIG. 7 are applied to theleads 66. Note that in order to produce the numeral 2, the second, sixthand seventh areas 60, 64 between the strips 58 and 62 in column I-I musthave potentials applied thereacross. Con sequently, the waveform Hcomprises a first positive pulse in the frame period coinciding with thenegative pulse in waveform B, a second positive pulse coinciding withthe negative pulse in waveform F, and a third positive pulse coincidingwith the negative pulse in waveform G. As the pulses on leads 68 sweepthrough one frame period, those which coincide with positive pulses inwaveform II will cause the second, sixth and seventh areas to becomeopaque. Similarly, in column I, it is necessary to render the first,fifth and seventh areas opaque. This is caused by having a positivepulse in waveform J coincide with a negative pulse in waveform A, apositive pulse in waveform J to coincide with a negative pulse inwaveform E and a positive pulse in waveform J to coincide with anegative pulse in waveform G. The various areas forming the numeral 2 ofFIG. 7 will not be continually opaque; however the sweeping action willoccur sufficiently rapidly so that a continual image will appear to thenaked eye. Any flicker effect appearing to the observer can be reducedby shortening the frame period and increasing the scanning frequency.

In FIG. 8, still another embodiment of the invention is shown whereinone of two transparent plates 96 is provided with a continuous layer oftransparent conducting material 98; while the other transparent plate 99is provided with a series of mutually insulated strips of transparentconducting material 100. The total configuration, when opaque,represents the numeral 8. Beneath the configuration 100 is a line or bar102 and to the right of the configuration is a dot 104 which forms adecimal point when a plurality of the arrays of FIG. 8 are placedside-by-side. The dot 104 is aligned with area 98A of layer 98; whilearea 988 is aligned with the bar 102. The various mutually insulatedconductive strips forming the configuration 100, in turn, are connectedthrough a plurality of mutually insulated strips of transparentconducting material 106 to external leads, not shown. Assuming, forexample, that it is desired to form the numeral 3, the plate 98 on oneside of the layer of liquid crystal material will be connected to asource of positive potential while the transparent strips on the otherside forming a 3 will be connected through leads 108 to a source ofnegative potential. If it is desired to place a-decimal point beside thenumeral, the lead connected to the spot 104 will be connected to thesame source of negative potential; and if it is desired to provide aline beneath the numeral, the lead connected to strip 102 will beconnected to the source of negative potential. In any case, only thoseportions on the plate 99 will appear opaque on a white background (orvice versa) which are connected to a source of potential of polarityopposite to that applied to the plate 98. As will be appreciated, aseries of the displays shown in FIG. 8 can be assembled in side-bysiderelationship to provide any desired number of digits.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

I claim as my invention:

1. A device for converting electrical intelligence into an optical imagecomprising a layer of liquid crystal material nematic at roomtemperature and disposed between transparent parallel plates, both ofsaid plates being coated with films of transparent con ducting material.at least one of said plates being coated on only selected areas thereofwith films of transparent conducting material, means for effecting atwisted nematic structure in said layer of liquid crystal material,polarizers on opposite sides of said layer of liquid crystal materialand extending essentially parallel to said plates to provide a sandwichstructure through which light can pass. and means for establishing apotential difference between films on the respective plates such thatsome areas ofthe sandwich structure will transmit light while otherswill not to thereby form an optical image.

2. The device of claim 1 wherein said liquid crystal material comprisesa mixture of 40 percentbis-(4-noctyloxybenzal)-2-chlorophen'ylenediamine, 50 percentplmethylbenzal-p-n-butylaniline and percentp-cyanobenzal-p'n-butylaniline.

3. The device of claim 1 wherein said polarizers comprise polarizingsheets on the sides of said plates opposite said liquid crystalmaterial.

4. The device of claim 1 wherein the crystal material is nematic and ofpositive dielectric anisotropy.

5. The device of claim 1 wherein one of said polarizers polarizes lightat right angles to the other, whereby light will pass through theentirety of said sandwich structure with no electrical potentialestablished between said films, said films acting to block the passageof light through selected areas of said sandwich structure uponapplication of a potential difference between said films.

6. The device of claim 1 wherein said films on the respective plates arein the form of a desired image.

7. The device of claim 1 wherein said films on the respective plates arein the form of mutually insulated strips which cross each other.

8. The device of claim 9 including means for applying pulses to themutually insulated strips on the respective plates.

9. The device of claim 10 including means for applying pulses of onepolarity in succession to the strips on one of said plates, and meansfor simultaneously and selectively applying pulses of the oppositepolarity to the strips on the other of said plates, each of said pulsesof the opposite polarity being in phase with at least one of the pulsesof said one polarity, whereby light transmitting characteristics of saidsandwich structure will be varied at selected crossings of the strips onthe respective plates to fonn an optical image.

10. The device of claim 11 wherein said pulses of one polarity and saidpulses of the opposite polarity occur during a frame period, andincluding means for continually repeating said frame period.

11. The device of claim 1 wherein one of said plates is coated withmutually insulated film portions of transparent conducting materialarranged to form any one of a plurality of images, the other of saidplates being coated with an unbroken area of conducting material whichcovers the entire area of the portions on the opposite plate, and meansfor selectively establishing a potential between the film on said otherplate and selected ones of said portions on said one plate.

a t t t u

2. The device of claim 1 wherein said liquid crystal material comprisesa mixture of 40 percentbis-(4''-n-octyloxybenzal)-2-chlorophenylenediamine, 50 percentp-methylbenzal-p''-n-butylaniline and 10 percentp-cyanobenzal-p''-n-butylaniline.
 3. The device of claim 1 wherein saidpolarizers comprise polarizing sheets on the sides of said platesopposite said liquid crystal material.
 4. The device of claim 1 whereinsaid polarizers comprise dichroic films.
 5. The device of claim 4wherein said dichroic films are deposited on said conducting films andare in contact with the liquid crystal material.
 6. The device of claim1 wherein the crystal material is nematic and of positive dielectricanisotropy.
 7. The device of claim 1 wherein one of said polarizerspolarizes light at right angles to the other, whereby light will passthrough the entirety of said sandwich structure with no electricalpotential established between said films, said films acting to block thepassage of light through selected areas of said sandwich structure uponapplication of a potential difference between said films.
 8. The deviceof claim 1 wherein said films on the respective plates are in the formof a desired image.
 9. The device of claim 1 wherein said films on therespective plates are in the form of mutually insulated strips whichcross each other.
 10. The device of claim 9 including means for applyingpulses to the mutually insulated strips on the respective plates. 11.The device of claim 10 including means for applying pulses of onepolarity in succession to the strips on one of said plates, and meansfor simultaneously and selectively applying pulses of the oppositepolarity to the strips on the other of said plates, each of said pulsesof the opposite polarity being in phase with at least one of the pulsesof said one polarity, whereby light transmitting characteristics of saidsandwich structure will be varied at selected crossings of the strips onthe respective plates to form an optical image.
 12. The device of claim11 wherein said pulses of one polarity and said pulses of the oppositepolarity occur during a frame period, and including means forcontinually repeating said frame period.
 13. The device of claim 1wherein one of said plates is coated with mutually insulated filmportions of transparent conducting material arranged to form any one ofa plurality of images, the other of said plates being coated with anunbroken area of conducting material which covers the entire area of theportions on the opposite plate, and means for selectively establishing apotential between the film on said other plate and selected ones of saidportions on said one plate.